Oral self-administration of phencyclidine (PCP) is currently being studied in eight rhesus monkeys working in an operant conditioning situation. Phencyclidine was established as a reinforcer with water concurrently available for all eight monkeys, under a range of fixed ratio (FR) values (e.g. FR 4 to FR 64). Phencyclidine was also reliably selected over water at wide range of concentrations (0.0125 to 1.0 mg/ml). A concentration-response study conducted with a PCP analog, PCE, revealed that PCE also served as a reinforcer over a similar range of concentrations, but PCE was slightly less potent than PCP. Another variable found to control PCP-maintained behavior was percent of free feeding bodyweight. Under conditions of partial food deprivation, when body weights were reduced to 85%, PCP (0.25 mg/ml) served as a more potent reinforcer. However at a higher PCP concentration, the effect of body weight and feeding conditions was considerably reduced. Another major area of this research concerns interactions of PCP with other drugs. Current results show that lower pentobarbital doses (2.5 mg/kg i.m.) increase responding for orally-delivered PCP, intermediate doses (5 mg/kg i.m.) have no effect and higher doses (10 mg/kf i.m.) decrease PCP-maintained responding. Overall, PCP appears to be a highly effective reinforcer for rhesus monkeys using our oral procedures. The establishment of this model has allowed for the study of many variables and interactions among variables that control drug self-administration behavior.